Increasing Biogas Production from Maize Silage by Ultrasonic Treatment

Abstract

Maize silage is one of the most commonly used substrates in biogas plants all over Europe today. However, a considerable part of it is not biologically converted into biogas during anaerobic digestion process (AD). This is caused by content of materials unsuitable for AD (e.g. lignin) and substances requiring very long residence time to be decomposed under anaerobic conditions (which would be ineffective from economical point of view). In case of such complex phytomass, the rate-limiting step of AD is hydrolysis of biomacromolecules (mainly polysaccharides). Cavitation induced by ultrasonic treatment of substrate causes increase of particles’ specific area, cell lysis and sonochemical reactions, resulting in splitting of complex organic compounds due to formation of radicals. As a consequence, faster and more efficient conversion of substrate into methane is achieved. To evaluate effect of sonication on biogas production, parallel batch experiments in CSTR bioreactors were carried out. Assessment of substrate disintegration caused by sonication was based on measurements of Chemical oxygen demand (COD) in liquid phase of substrate samples. The biogas and methane CH4 yields were determined by continuous measurement of biogas flow rate and composition. The resulting biogas production enhancement was 13 29.5%, methane yield was increased by 16.9 – 29.5 %. The key evaluation of ultrasonic treatment process is the energy balance. Its results proved its suitability from the environmental point of view.